<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        body * {
            border: 1px solid red;
        }
    </style>
</head>
<body>
<!--
      块元素：div，h1--h6,p,ul,li,ol,dl,dd,dt,header,nav,footer,section,article,aside,

      行内元素：a，span，strong,em,mark,img,time
-->
<!--h标签对搜索引擎良好，h1一个页面最多最好一个-->
<div>div</div>
<a href="">a</a>
<span>span</span>
<h1>h1</h1>
<h2>h2</h2>
<h3>h3</h3>
<h4>h4</h4>
<h5>h5</h5>
<h6>h6</h6>
<p>p</p>
<strong>strong</strong>
<em>em</em>
<ul>
    <li>li</li>
</ul>
<ol>
    <li>li</li>
</ol>
<dl>
    <dt>dt</dt>
    <dd>dd</dd>
</dl>

<mark>mark</mark>
<img src="1.jpg">

<header>
    header
</header>
<nav>nav</nav>
<footer>footer</footer>
<section>section</section>
<article>article</article>
<aside>aside</aside>
<time>time</time>
</body>
</html>